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Valmet biosludge treatment system

The pulp and paper industry has taken important steps to decrease emissions and as new solutions become available and the mills continue to upgrade, the trend continues towards better use of natural resources and minimized environmental impact. The Valmet biosludge treatment system offers a cost-effective way to dispose of biosludge. This helps to keep the secondary water treatment working at an optimum and gives a positive ROI, compared to traditional ways to handle biosludge.

Efficient wastewater treatment in pulp mills – safe removal of biosludge

Cleaning of pulp mill effluent is typically done with a primary stage that removes suspended solids and a secondary stage that lowers the amount of organic matter through biological degradation. To maintain high efficiency in the secondary stage, biosludge (also known as secondary sludge) is continually removed from the basins of the secondary water treatment. The amount of biosludge varies with mill conditions but can be in the range of 5-15 kg (dry solids) per ton of pulp.

Biosludge is often difficult to dispose of because of the heavy odor that is released during decomposition. It is difficult to dewater the sludge, and this makes landfilling (no longer used in European countries) and incineration in a power boiler costly. Incineration of biosludge can, besides loss of thermal efficiency and steam generation, lead to combustion stability problems, corrosion and higher emissions.

The Valmet biosludge treatment system

The Valmet system offers a cost-effective solution.

The sludge is treated to improve dewatering, mixed into the black liquor and evaporated in the evaporators. The process has very low impact on pulp mill processes, is safe for operators and the environment, needs little maintenance and is also easy to control. 

Several European mills have chosen to install the system and one of them even returned to Valmet to upgrade their installation as the mill had expanded.

When it comes to emissions of NOx from the recovery boiler, adding biosludge to the black liquor has not had any significant impact on emissions. In some cases, it has been necessary to adjust the recovery boiler air to return the levels to normal but no rebuilds have been required.

 

For further information, please contact Kai Lüder at Valmet:
kai.lyder at valmet.com, telephone: +46 31 50 10 00.